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Today Rebecca is 34 years old

This topic has 4 expert replies and 1 member reply
boomgoesthegmat Senior | Next Rank: 100 Posts Default Avatar
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Today Rebecca is 34 years old

Post Mon Apr 25, 2016 2:32 pm
Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca’s age is twice her daughter’s age?
A) 10
B) 14
C) 18
D) 22
E) 26

Answer: C

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Post Thu Jan 04, 2018 8:53 am
boomgoesthegmat wrote:
Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca’s age is twice her daughter’s age?
A) 10
B) 14
C) 18
D) 22
E) 26
We are given that Rebecca is 34 and her daughter is 8. We can let n = the number of years before Rebecca is twice as old as her daughter. At that time, Rebecca will be (34 + n) years old and her daughter will be (8 + n) years old, and Rebecca will be twice her daughter’s age:

34 + n = 2(8 + n)

34 + n = 16 + 2n

18 = n

Answer: C

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Matt@VeritasPrep GMAT Instructor
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Post Wed Apr 27, 2016 2:18 pm
Let's put it in words first, then assign variables.

Rebecca's Age + Some Number of Years = 2 * (Daughter's Age + Same Number of Years)

We know the two initial ages, and we can call the Number of Years y.

34 + y = 2 * (8 + y)

34 + y = 16 + 2y

18 = y

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Post Mon Apr 25, 2016 3:54 pm
boomgoesthegmat wrote:
Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca’s age is twice her daughter’s age?
A) 10
B) 14
C) 18
D) 22
E) 26

Answer: C
I think the best (i.e., fastest) approach is to TEST the answer choices.
However, for those who prefer using algebra, here's an algebraic approach:

Let x be the number of years from today.
So, x years in the future, Rebecca's age will be 34 + x
And, x years in the future, her daughter's age will be 8 + x

We want Rebecca’s future age to be twice her daughter’s future age.
We can create the following "word equation": (Rebecca’s future age) = 2(daughter’s future age)
Or we can write: (34 + x) = 2(8 + x)
Expand to get: 34 + x = 16 + 2x
Solve to get: x = 18

Answer: C

Cheers,
Brent

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Post Mon Apr 25, 2016 4:07 pm
Hi boomgoesthegmat,

Certain questions in the Quant section can be solved rather easily by TESTing THE ANSWERS.

Here, we know that Rebecca's current age is 34 and her daughter's age is 8. We're asked how many years will need to pass by before Rebecca's age is exactly TWICE her daughter's age. Since the 5 answer choices are all numbers, we can TEST them until we find the match...

A) 10 years
Rebecca will be 44
Daughter will be 18
44 is NOT double 18

B) 14 years
Rebecca will be 48
Daughter will be 22
48 is NOT double 22

C) 18 years
Rebecca will be 52
Daughter will be 26
52 IS double 26
This must be the answer.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

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OptimusPrep Master | Next Rank: 500 Posts
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Post Mon Apr 25, 2016 8:16 pm
boomgoesthegmat wrote:
Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca’s age is twice her daughter’s age?
A) 10
B) 14
C) 18
D) 22
E) 26

Answer: C
Testing values in an efficient way to solve this question, but in such problems, I always prefer going for equations rather that testing values.

Assume that Rebecca is twice her daughter's age after x years.
Hence we have, 34 + x = 2*(8 + x)
34 + x = 16 + 2x
x = 18

Correct Option: C

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